Here I repair a Macbook Air 820-3209 logic board that had no power, then no CPU vcore, then no backlight after a liquid spill.
First I troubleshoot PP5V by running 3.3v to its enable pin, and the board turns on. The next day this wire came off, and it still turned on anyway, meaning the board fixed itself via psychic magic while sitting on my table that evening.
Then it would turn on, but it didn't do anything. No chime, nothing on the screen, just blank. I saw no CPU vcore, so I troubleshooted and found that a piece of the board was hanging on by a red trace. I replaced it and ran a wire from the resistor to a probe point on the board since the solder pad for the component was gone, and now it turns on and chimes.
....but there's no backlight :( I replaced the backlight fuse and it was good. I didn't bother measuring the backlight fuse, I just looked at it and said this got to go!
At the end we have a working board. :)
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